1. Field of the Invention
This invention relates generally to handheld vacuum cleaners, and more particularly to a dirt-cup type filter for a handheld vacuum cleaner.
2. Description of the Related Art
In the vacuum cleaner art, distinctions are made between handheld and upright vacuum cleaners. Upright vacuums are normally large devices that rest upon the floor at all times and are moved by rolling. Uprights are too heavy to be lifted easily. Handheld vacuums, on the contrary, are designed to be lifted and carried easily by an operator to sweep stairs, shelves, windowsills, and other surfaces above the ground.
The typical filters used in upright vacuum cleaners include bags and dirt cup filters. Bags are made of sheets of filtration material sewn or otherwise joined together near an opening through which air is drawn from the area being vacuumed. Dirt cup filters are cylindrical or frustoconical “cups” that have filtration material around the curved sidewall. Some dirt cup filters have HEPA rated filter material, which has very fine pores, and therefore the loading of the filter with large debris can significantly decrease the life of the filter.
Dirt cup filters are often used with upright vacuums that take advantage of cyclonic action, to reduce the loading of the filter with large debris. Cyclonic action is a principle in which dirty air swirls around in a chamber before passing through a filter to allow particles to settle out during the swirling action.
Handheld vacuum cleaners typically use bag filters, because they are not always oriented in a way which enables them to take advantage of cyclonic action. Furthermore, there is rarely enough space in a small handheld vacuum cleaner to accommodate the large chamber needed for cyclonic action of the air/debris combination.
Therefore, the need exists in handheld vacuum cleaners for a filter that has a long life due to a configuration that prevents it from getting loaded with large debris too rapidly.